Exoplanet Explorer: Poltergeist

May 10, 2017

Today’s post is part of a semi-regular series here on Planet Pailly exploring exoplanets: planets orbiting stars other than our Sun. Today, we’re exploring the exoplanet:


In 2015, our friends at the International Astronomy Union gave in to public pressure and finally started assigning actual names to exoplanets. Thus, the exoplanet designated PSR B1257+12 c is now known as Poltergeist.

Poltergeist is actually the very first exoplanet we humans ever discovered. It’s approximately four times as massive as Earth, has an orbital period of 66 days, and is located in a star system roughly 2,300 light-years away in the constellation Virgo.

It’s hard to say much else about a planet so far away from us, but based on what we do know at this point, I’m willing to bet Poltergeist is a barren rock stripped of any appreciable atmosphere and depleted of all or almost all of its volatiles.

That’s because Poltergeist’s sun is no ordinary star. It’s a pulsar: the tiny, rapidly-spinning, gamma radiation flashing remnants of a star that went supernova. As of 2015, the I.A.U. has named this pulsar Lich, and there are two other planets in the Lich System: Draugr and Phobetar. The official naming scheme for this system is apparently the undead.

  • Lich: an undead thing with magic powers to control other undead things.
  • Draugr: a reanimated corpse from Norse mythology.
  • Poltergeist: a ghost, especially a noisy and troublesome ghost.
  • Phobetor: the ancient Greek god of nightmares.

According to this paper (published in 1993, right after the discovery of Poltergeist and Phobetor but before the discovery of Draugr), there are quite a few scenarios that could explain how a pulsar like Lich ended up with its own planets. We can’t say for sure which scenario is correct, but all the most likely scenarios have one thing in common: the planets formed after the supernova.

Perhaps the planets that existed before the supernova were destroyed, and Poltergeist and company re-coalesced from the rubble (this paper from 2015 seems to rule that possibility out). Or perhaps Lich was once part of a binary system, and the planets formed after Lich ripped its companion star apart. Or maybe Lich is the product of a violent merger of two white dwarf stars, or a white dwarf and a neutron star, with the planets forming from matter the got spewed into space during the merger (this is reportedly the most plausible scenario).

So it would seem Poltergeist and the other planets of the Lich System really are the ghosts left over by some cataclysmic event (even if we’re not certain which specific cataclysm occurred) which is why their creepy, Halloween-style names are so appropriate.